Comparative psychology refers to the scientific study of the behavior and mental processes of non-human animals, especially as these relate to the phylogenetic history, adaptive significance, and development of behavior. Research in this area addresses many different issues, uses many different methods and explores the behavior of many different species from insects to primates.[1][2]

Comparative psychology is sometimes assumed to emphasize cross-species comparisons, including those between humans and animals. However, some researchers feel that direct comparisons should not be the sole focus of comparative psychology and that intense focus on a single organism to understand its behavior is just as desirable; if not more so. Donald Dewsbury reviewed the works of several psychologists and their definitions and concluded that the object of comparative psychology is to establish principles of generality focusing on both proximate and ultimate causation. [3]

Using a comparative approach to behavior allows one to evaluate the target behavior from four different, complementary perspectives, developed by Niko Tinbergen.[4] First, one may ask how pervasive the behavior is across species (i.e. how common is the behavior between animal species?). Second, one may ask how the behavior contributes to the lifetime reproductive success of the individuals demonstrating the behavior (i.e. does the behavior result in animals producing more offspring than animals not displaying the behavior)? Theories addressing the ultimate causes of behavior are based on the answers to these two questions.

Third, what mechanisms are involved in the behavior (i.e. what physiological, behavioral, and environmental components are necessary and sufficient for the generation of the behavior)? Fourth, a researcher may ask about the development of the behavior within an individual (i.e. what maturational, learning, social experiences must an individual undergo in order to demonstrate a behavior)? Theories addressing the proximate causes of behavior are based on answers to these two questions. For more details see Tinbergen's four questions.

History

The 9th century scholar al-Jahiz wrote works on the social organization and communication methods of animals like ants.[5] The 11th century Arabic writer Ibn al-Haytham (Alhazen) wrote the Treatise on the Influence of Melodies on the Souls of Animals, an early treatise dealing with the effects of music on animals. In the treatise, he demonstrates how a camel's pace could be hastened or retarded with the use of music, and shows other examples of how music can affect animal behavior, experimenting with horses, birds and reptiles. Through to the 19th century, a majority of scholars in the Western world continued to believe that music was a distinctly human phenomenon, but experiments since then have vindicated Ibn al-Haytham's view that music does indeed have an effect on animals.[6]

Charles Darwin was central in the development of comparative psychology; it is thought that psychology should be spoken in terms of "pre-" and "post-Darwin" because his contributions were so influential. theory led to several hypotheses, one being that the factors that set humans apart, such as higher mental, moral and spiritual faculties, could be accounted for by evolutionary principles. In response to the vehement opposition to Darwinism was the "anecdotal movement" led by George Romanes who set out to demonstrate that animals possessed a "rudimentary human mind".[3] Romanes is most famous for two major flaws in his work: his focus on anecdotal observations and entrenched anthropomorphism.[1]

Near the end of the 19th century, several scientists existed whose work was also very influential. Douglas Alexander Spalding was called the "first experimental biologist",[3] and worked mostly with birds; studying instinct, imprinting, and visual and auditory development. Jacques Loeb emphasized the importance of objectively studying behavior, Sir John Lubbock is credited with first using mazes and puzzle devices to study learning and Conwy Lloyd Morgan is thought to be "the first ethologist in the sense in which we presently use the word".[3]

Throughout the long history of comparative psychology, repeated attempts have been made to enforce a more disciplined approach, in which similar studies are carried out on animals of different species, and the results interpreted in terms of their different phylogenetic or ecological backgrounds. Behavioral ecology in the 1970s gave a more solid base of knowledge against which a true comparative psychology could develop. However, the broader use of the term "comparative psychology" is enshrined in the names of learned societies and academic journals, not to mention in the minds of psychologists of other specialisms, so the label of the field is never likely to disappear completely.

A persistent question with which comparative psychologists have been faced is the relative intelligence of different species of animal. Indeed, some early attempts at a genuinely comparative psychology involved evaluating how well animals of different species could learn different tasks. These attempts floundered; in retrospect it can be seen that they were not sufficiently sophisticated, either in their analysis of the demands of different tasks, or in their choice of species to compare.[1] However, the definition of "intelligence" in comparative psychology is deeply affected by anthropomorphism, and focuses on simple tasks, complex problems, reversal learning, learning sets, and delayed alternation are plagued with practical and theoretical problems.[1] In the literature, "intelligence" is defined as whatever is closest to human performance and neglects behaviors that humans are usually incapable of (e.g. echolocation).[7] Specifically, comparative researchers encounter problems associated with individual differences, differences in motivation, differences in reinforcement, differences in sensory function, differences in motor capacities, and species-typical preparedness (i.e. some species have evolved to acquire some behaviors quicker than other behaviors).[1]